Devicetree add-on

[Marco Felsch]

Hi Alexander,

thanks for reaching out to the ML.

On 25-01-29, Alexander Shiyan wrote:
> Hello All.
> 
> The question arose whether it is possible to load an add-on into
> devicetree, but NOT through an overlay,

Why not dt-overlays?

> i.e. as a full-fledged dtb?
> Ideally, it should look like this: the main ENTRY_FUNCTION() loads the
> base tree, then,
> after initialization in device_initcall(), the board modification is
> determined and the full devicetree
> written for this variant is loaded.

Sounds exactly like a dt-overlay use-case. As it sounds to me you do
have common base for your platform/product family. This would be your
base-dtb loaded for every product. Later on you need to apply the
overlays accordingly.

E.g. for the platform family I'm currently working with we do the
following:

base-dt:
--------
/ {
	feat_a: feature-device-a {
		compatible = "xyz,feature-device-a";
		...
		...
		status = "disabled";
	};

	feat_b: feature-device-b {
		compatible = "foo,feature-device-b";
		...
		...
		status = "disabled";
	};
};

feat-a-dto:
-----------
&feat_a {
	status = "okay";
};

feat-b-dto:
-----------
&feat_b {
	status = "okay";
};

This way we define the whole node within the base-dt and the overlays
only enable it. This makes the overlays very straightforwward and you
still have the opportunity to reconfigure the device-node if you really
have to.

Regards,
  Marco